Hitherto, in the above-stated type of hot water storage tank unit, a heat insulator has been placed on the outer peripheral surface of the hot water storage tank to reduce the amount of heat transfer.
For example, there has been proposed a configuration in which a vacuum heat insulator that is expensive but has a high heat insulation property and can suppress heat transfer to a small volume is applied to a part of this configuration where the amount of heat transfer is large, while a heat insulator that is less expensive than the vacuum heat insulator but is inferior to the vacuum heat insulator in heat insulating property is applied to the other parts, so that the cost and product size are thereby reduced (see, for example, Patent Literature 1).
There has been proposed a configuration in which the vacuum heat insulator is applied only to a dimensionally constrained part, a heat insulator that is inferior to the vacuum heat insulator in heat insulating property but is less expensive than the vacuum heat insulator is applied to dimensionally unconstrained parts, and both the cost and product size are thereby reduced (see, for example, Patent Literature 2).